An Anion Selective Aminocyclodextrin Ion Channel: Ion Selectivity, pH Sensitivity and Potential as a Scaffold for Light Gating

164 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006.The synthesis and characterization of a highly active ion channel mimic and a photocleavable tether as a potential light activated switch is described. Signal activated ion channels are attractive for use in applications such as biosensors and nano-switches. A new photocleavable o-nitrobenzyl dimeric tether has been developed as a potential trigger for the photoactivation of the ion channel. The utility of the tether was demonstrated by functionalizing primary, secondary and benzylic alcohols with the tether and subjecting the resulting ethers to photolysis. The photolysis of the tethered ethers was found to be extremely efficient and the corresponding alcohols were isolated in 79-100% yields. Comparison with the corresponding monomeric ethers indicated superior yields for the ethers functionalized with the dimeric tether. An aminocyclodextrin ion channel was synthesized from heptaiodinated beta-cyclodextrin and amine functionalized pentabutylene glycol chains. Ion transport through the channel gauged using 23Na NMR and fluorescence spectroscopy indicated high ion transport activity, comparable to natural ion channels. The fluorescence studies also indicated that the ion channel was highly anion selective with anion transport rates being ClO4- > I- > NO3- > Br- > Cl-. The rates for the transport of ClO4 -, I-, NO3- and Br- ions were ca. 20, 9, 3.1 and 2.6 times that for Na + ions, respectively. The anion selectivity for the ion channel is attributed to the presence of seven amino groups conferring positive charge at the pore opening of the ion channel. The ion transport rates and the ion selectivity of the ion channel were found to be pH dependent. At high pH values fast transport rates for Na+ and X- ions was demonstrated, while at low pH higher selectivity between ions was observed.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD